The invention relates to a measuring system for the monitoring of residual dust for safety vacuum cleaners.
Similar measuring arrangements for the monitoring of the dust concentration in the exhaust air in vacuum cleaners are already known and these employ physical measuring principles such as, for example, the measurement of the differential pressure or of the radiation reflection.
In differential pressure measurement the cc prevailing pressure before the filter unit is compared with the prevailing pressure after the filter unit or after the motor, the differential pressure not being allowed to pass below a threshold value. With a non-defective and unfouled filter the admissible differential pressure is least, the differential pressure increases with increasing blockage of the filter. If the filter cracks, then an inadmissible pressure balance between the chambers before and after the filter arises and the differential pressure falls below the admissible threshold value in the direction of zero differential pressure. The undershooting of the differential pressure with a cracked filter, but also the exceeding of the differential pressure with a blocked filter, can be used as alarm means for purposes of the motor control.
A disadvantage in the measuring principle with the differential pressure method is that the pressure fluctuations, caused by running fluctuations of the motor because of changing volumes and speeds of the suction medium and by differing blocking and quality of the filter, are nevertheless so high that an exact registration of the undershooting or exceeding of the threshold value can be achieved only inadequately especially in the case of low differential pressures.
DE-GM 92 09 407.4 discloses a detection device of filter breakage in vacuum cleaner arrangements, which device uses the principle of infrared radiation reflection for the particle measurement in the exhaust air. In the exhaust air channel of a vacuum cleaner arrangement there are arranged an infrared sender and an appertaining infrared receiver angularly offset to one another on the circumference of the exhaust air channel, long-wave energy being radiated into the exhaust air channel by the infrared sender. This infrared radiation is then partly reflected on the dirt particles flowing through in such manner that the reflection radiation is registered over the infrared receiver offset, for example, by 90xc2x0 to the infrared sender.
The energy supplying and the measuring signal preparation occurs in an evaluating electronic system connected with the sender and receiver. The measuring field is defined by the overlapping of the respective input and output jet cone.
On concentration rise of the dust particles in the exhaust air channel the IR energy irradiated by the sender is reflected (amplified) on the particles and measured in the receiver and in this manner a threshold value preset in the evaluating electronic system can be overstepped, which threshold value triggers an alarm and/or brings the motor to a standstill. In this manner, a filter breakage is measured and displayed, in order to avoid health-threatening particle emissions into the environmental air, by manual or automatic switching off of the suction motor, and to make possible a filter change in proper time.
A disadvantage in the measuring principle with infrared radiation reflection for the residual dust particle measurement is that the optical system can be very easily soiled, both that of the IR sender and also that of the IR receiver, whereby the measurement signal is falsified, since the dust particles on sender and receiver likewise absorb and reflect IR energy; these dirt particles, however, are not to be measured, since, after all, they do not reflect the actual flow state in the exhaust air channel. This falsification of the measurement signal by fouling can be poorly compensated, since the degree of fouling is constant neither in time nor locally, and therewith cannot be exactly defined. Thereby for an effective measurement, whether technical and/or computational, compensation is possible only very defectively.
A further disadvantage of the measuring principle with infrared radiation reflection for residual dust particle measurement is that measurement is restricted to the focusing range of the sender/receiver, i.e., the measurement field defined by the overlapping of the radiation cones of sender and receiver does not cover the entire cross-section of the outlet tube, whereby outside of the measuring field no particle measurement takes place, which likewise leads to an undefined, poorly compensatable falsification of the measurement signal.
The purpose for this invention, therefore, is to provide a measuring system for residual dust monitoring in safety vacuum cleaners in such manner that the above-mentioned disadvantages of the state of the art are reduced or even eliminated. Specifically, it is found that the measuring system is more sturdy resulting in a more dependable construction. It is also found that the system provides more accurate measurements in the case of low particle concentration in the exhaust air.
Here the measuring system, on the one hand, is to be less subject to fouling and therewith to make possible longer maintenance intervals; on the other hand, it is also meant to make possible a more accurate measurement of the particle concentration in the exhaust air, in order to give more exact information about the state of the filter, as to whether a defect is present or not. It is also to make it possible to determine low dust concentrations in the exhaust air.
For the solution of the problem posed there serves the technical teaching of the present invention.
An essential feature is that, according to the invention, the measuring system of the residual dust monitoring in safety vacuum cleaners provides for at least one measuring electrode mounted upstream behind the filter unit. The measuring element transmits a current signal to a measurement value processing unit. The current signal is produced by contact tension between measuring electrode and particles and depends on the particle concentration.
There arises here a contact voltage through intensive contact of the dust particles carried along in the carrier medium (air) with the material of the measuring electrode. If the dust particles consist of a material which is materially different from the material of the measuring electrode, then there occurs a passing-over of electrons which flow off to the lower potential as a function of the contacting particles and therewith of the particle concentration in the exhaust air. This holds for both electrically conducting particles and electrically insulating particles. With electrically conducting particles the cause of the charge separation lies in the differing emergence work in comparison to the measuring electrode, and with electrically insulating particles the charge separation lies in the different electron affinity in comparison to the measuring electrodes.
In a preferred form of execution of the measuring system for residual dust monitoring for safety vacuum cleaners according to the invention, it is provided that at least one measuring electrode is arranged downstream within the outlet tube behind the filter and behind the turbine, preferably in the end zone of the outlet tube. Also, it must be possible to arrange the measuring electrode in the vicinity of the turbine in the outlet tube or in the motor block of the turbine itself.
In a further form of execution of the inventive measuring system of the residual dust monitoring in safety vacuum cleaners it is provided that at least one measuring electrode is mounted downstream behind the filter or in front of the turbine, preferably directly on or in the near zone of the filter outlet surface. The measuring electrode can, however, also be arranged in an intermediate tube or an intermediate chamber between filter and turbine or else in the vicinity of the turbine in the motor block.
It is preferred that the measuring electrode cover the entire flow cross-section, but in such manner that the flow resistance in the safety vacuum cleaner is only inappreciably increased and thus the efficiency of the vacuum cleaner is not impaired by the measuring arrangement.
Preferably, therefore, at least one measuring electrode covers the entire filter output surface, the cross-section of the intermediate tube, or the intermediate chamber between filter and turbine, or the entire cross-section of the outlet tube.
In a preferred form of execution the measuring electrode is constructed in grid form, similar to a mesh wire or perforated plate, and it lies with its mantle surface firmly on the inner circumference of the tube or of the chamber.
The grid-form measuring electrode can be bounded by an annular element around the mantle surface, in which case preferably the annular element consists of the same material as the measuring electrode. It can, however, also consist of flexible plastic, into which the measuring electrode is cast and is thrust with clamping effect into the outlet tube. The fixing into position of the measuring electrode can occur over a releasable or unreleasable connection. It is preferred, however, that the fixing is over a releasable screw, a rest or clamping connection, or a welding connection.
If the measuring electrode lies directly on the filter outlet surface or in its vicinity, then it has about the same form as the filter. Therefore, for example, a cylindrical/tubular form or disk form can be joined with the filter on its face side and/or mantle surface.
Several grid-type measuring electrodes can be provided, which again transmit their measuring signal to a measuring value processor. Here there can also be measured information about the level of the particle concentration, the distribution of the particle concentration over the cross-section of the outlet tube, and therewith the position of the filter defect can be determined. This holds, of course, only for a measuring electrode that is located between filter and turbine, since the particles in the turbine substantially change their flow path, so that a correlation between measuring point and particle concentration behind the turbine or also in the vicinity in front of it is no longer possible.
Through the fact that the dust particles can be charged in a certain manner before their contact with the measuring electrode already in the inlet channel, in the dust chamber (housing), in their passage through the filter and the turbine and in the outlet channel, the dust particles are preferably discharged before contact with the measuring electrode in order to minimize measurement value falsifications.
This takes place by grounding of the parts of the safety vacuum cleaner which first come in contact with the particles before the latter encounter the measuring electrode.
As a rule a grounding of the turbine housing suffices which with low protection demands is directly grounded, and in the case of high protective requirements is laid on artificial ground, therefore over protective impedances with one of the phases, or is electrically conductively connected with one of the phases or with the zero conductor of the turbine motor.
It is also possible, instead of this or additionally, to ground the housing of the safety vacuum cleaner, which is mostly standardly provided also for operator safety reasons when the housing is not insulatingly constructed.
Under the above-mentioned protection requirements there are to be understood contact and foreign-body protection, water protection and explosion protection, in which context there fall under explosion protection both the use of the apparatus in a danger zone (for example tank location zone), and also the use of the apparatus with hazardous substances (for example drawing-off of explosive gases and fluids).
Since the electrical currents to be measured in the measuring electrode, by reason of the contact voltage through intensive contact of the dust particles carried along in the carrier medium (air) with the material of the measuring electrode, amount merely to a few nano-amperes (nA, 10xe2x88x929), for the further processing of the measuring signal, this signal must first be amplified.
Here a differential amplification offers itself, for example over a linear, inverting, differentiating operation amplifier, which inverts the measuring signal and amplifies it in respect to potential ground or artificial ground, correspondingly into the milli-ampere range (mA, 10xe2x88x923).
Of course all possible constructions of an operation amplifier can be provided, such as adders, substracters, integraters, differentiators and all combinations of these, depending on what is to be measured and how the reckoning is to be performed.
It is obvious that this operation amplifier is preferably accommodated in a microchip and/or on a microprocessor which, for example, also fulfills still other assignments, such as, forexample the turbine regulation or other measuring, controlling and regulating assignments. It is possible, for example, for corresponding measurement values or indications to be issued on displays on the apparatus or only in case of disturbance.
This operation amplifier, microchip or microprocessor can then be connected over a usual interface with a personal computer or another data processing apparatus in order to coordinate measuring, control and regulating problems or in order to read out from the storage unit of the microchip or of the microprocessor, for example for statistical purposes. There can also occur a calibration over the PC, in which the threshold values for the further processing of the measurement signal are input, such as for example triggering of the alarm or switching on and off of the turbine.
If the filter unit is defective (for example burst or torn), then the particle concentration in the exhaust air stream rises rapidly and many more particles contact the measuring electrode and therewith the current flow rises away from the measuring electrode, and therewith the evaluating unit engaged on outlet side in the amplifier stage. Here then the measured value (actual value) is compared with the Oat threshold value (desired value) and then an optical and/or acoustic alarm signal is given. In addition to this or as a replacement for this the turbine motor can be switched off automatically, which must be accomplished manually in the case of the exclusive optical and/or acoustic alarm signal.
The present invention is intended to detect an ever so slight filter leakage, but this measuring arrangement can also be used to detect, to display the blocking of the filter, to trigger optical or acoustic alarm, to turn off turbines automatically or by hand, or to modify the action of the suction stream on them, or to change filters automatically or by hand. If, therefore, the filter is blocked, then a predetermined threshold value of the measuring signal is undershot and again and optical and/or acoustic alarm signal can be given or the turbine motor can be shut off. In distinction to the turbine standstill, in which measurement signal is registered, with blocked filter and switched-on turbine a slight particle concentration is still measurable.
In forms of execution of the safety vacuum cleaner with several independent filter units, by the exceeding of the preset threshold value internally and automatically, the suction medium can be led to another turbine with unused/nondefective filter unit and it is not until the last unused/nondefective filter is likewise used-up that an alarm is given.
In the forms of execution of the safety vacuum cleaner with several independent turbines, by the exceeding of the preset threshold value internally and automatically the suction medium can be led to another turbine with unused/nondefective filter unit and it is not until the last unused/nondefective filter is likewise used-up that an alarm is given.
For the reduction of disagreeable or health-harmful noises through the grid-form measuring electrode in the flow channel, it can be provided that in the region of the outlet channel a sound damper is provided, which influences the sound vibrations in such manner that the noise level is lowered below an admissible degree. Preferably the arrangement of the sound damper is made downstream at the free end of the outlet channel.
The inventive object of the present invention is yielded not only for the object of the individual patent claims, but also from the combination of the individual patent claims among one another.
All the indications and features disclosed in the documents, inclusive of the abstract, in particular the spatial formation represented in the drawings, are claimed as CA, essential to the invention insofar as they are novel individually or in combination with respect to the state of the art.